The invention relates to an apparatus for shifting a sewing position in a sewing machine which may be utilized in an automatic figured cloth sewing machine, for example.
In a sewing machine, a sewing position is shifted by the movement of either one of the body of the sewing machine or a fabric being sewn. For example, in an embroidery machine, a frame which is freely movable in either X- or Y-axis direction is used to support a fabric, and may be moved to enable a shifting of the sewing position in diverse directions.
A sewing machine in which a fabric is fixed while the body of the sewing machine is moved is disclosed, for example, in Japanese Utility Model Publication No. 32,626/1986. In a conventional sewing machine of this kind, support members such as rails are used to support a carriage in a manner so as to be freely movable in fore-and-aft direction under the control of a first drive mechanism, while the main body of the sewing machine is movably supported on the carriage by separate support members such as rails, with the main body being associated with another drive mechanism which drives it in a lateral direction.
The main body of the sewing machine generally comprises an arm assembly including a needle, a needle bar, an upper shaft and the like, and a bed assembly including a shuttle race, a shuttle bobbin, a lower shaft and the like. The arm and the bed assembly must be exactly matched in position. Since a fabric to be sewn is disposed between the arm and the bed assembly, the both assemblies are connected together by a stanchion, which is disposed laterally offset, so as to be integrally coupled together in a usual sewing machine. However, the stanchion stands in the way to the movement of the fabric. Accordingly, it is a usual practice to employ a design to assure a possible maximum distance between the needle position and the location of the stanchion in order to increase an area over which a sewing operation is enabled.
In the sewing machine disclosed in Japanese Utility Model Publication No. 32,626/1986, the arm and the bed assembly are separate from each other, and a mismatch in the position of the both assemblies is avoided by driving the both assemblies through a same stroke on the carriage. Frames disposed on the opposite sides of the carriage, namely, at its right and left ends thereof are used to support the arm and the bed assembly. By increasing the spacing between the left and the right end of the carriage, an arrangement is made to allow a relatively large area of movement of the arm and the bed assembly in the lateral direction.
However, in the conventional sewing machine described, since the arm and the bed assembly are mounted on the same carriage, the area of movement of the main body of the sewing machine in the lateral direction is limited by the presence of the frames located at the opposite ends of the carriage so as to be restricted to a zone inside the both frames. In actuality, because the frames located at the opposite ends of the carriage as well as the main body of the sewing machine have definite sizes, the area through which the main body of the machine can move in the lateral direction is considerably limited as compared to the dimension of the entire carriage.
If the carriage is made to a larger size in order to achieve a greater area of movement of the main body of the sewing machine in the lateral direction, the increased weight of the carriage prevents the speed of movement thereof from being increased, presenting a problem in respect of the sewing rate.